and 2% in Australia.6 Clearly, overnutrition is a serious health hazard world wide with signifi- cant financial expense. Our genetic pool has not been altered.
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Br J Sports Med 2000;34:86–93
Review
Physical activity mediates a healthier body weight in the presence of obesity Linda S Pescatello, Jaci L VanHeest
University of Connecticut, Storrs, CT, USA L S Pescatello J L VanHeest New Britain General Hospital, New Britain, CT, USA L S Pescatello Correspondence to: Dr L S Pescatello, University of Connecticut, School of Allied Health Professions, 359 Mansfield Road, U-2101, Storrs, CT 06269-2101, USA Accepted for publication 5 January 2000
Introduction In the last decade, the numbers of overweight (body mass index (BMI) >25 kg/m2) and obese (BMI >30 kg/m2) people have substantially increased in Canada, New Zealand, the United Kingdom, the United States, and Western Samoa.1 The prevalence of obesity in the United States has grown from 12.0% in 1991 to 17.9% in 1998.2 Recent reports indicate that overweight and obese adults now comprise the majority of the American population with 54.9% persons reporting a BMI >25 kg/m2. These alarming trends have led to the declaration of a global obesity epidemic.3 4 Overweight and obesity have become so common that they are replacing the more traditional health problems of undernutrition and infectious diseases as significant causes of poor health world wide.3 Excess weight is associated with numerous diseases and conditions including cardiovascular disease, Type 2 diabetes mellitus, hypertension, dyslipidaemia, osteoarthritis, sleep apnoea, gallbladder disease, infertility, and some cancers.5 The direct and indirect costs of obesity are considerable, with the associated expenses representing 7% of the national health care budget in the United States, 7% in the Netherlands, 4% in France, and 2% in Australia.6 Clearly, overnutrition is a serious health hazard world wide with significant financial expense. Our genetic pool has not been altered dramatically over the past 10 years. Consequently, the obesity epidemic can be attributed to environmental factors that promote physical inactivity and excessive intake of calories and high fat energy dense foods leading to a state of chronic positive energy balance.3 7 This long term excess energy availability contributes to insidious cumulative weight gain eventually resulting in overweight and obesity. Ecological studies support the notion that the decline in energy expenditure is the more probable cause of the obesity epidemic than overnutrition per se. In the United Kingdom, the prevalence of obesity increased over 150% between 1980 and 1997, whereas food intake per household decreased by 20% over this same time period.8 These observations support the contention that the significant increase in obesity world wide is due to greater relative declines in physical activity than increases in energy intake. As leisure time physical activity has remained constant over the previous two dec-
ades, the decrease in overall energy expenditure is thought to be due to significantly less participation in household work and daily routine physical activities.7 Therefore an essential vehicle for thwarting the obesity epidemic is to reduce sedentary behaviour by engaging in greater amounts of voluntary and spontaneous low to moderate physical activities which are accumulated throughout the day. The weight loss achieved through this approach may not be substantial enough to prevent overweight and obesity, and it may be negated by greater food intake. Nonetheless, moderate weight loss of 5–15% of body weight has been shown to result in significant health gains.9 10 Overweight and obesity have or are likely to become the norm in many societies world wide. A viable public health strategy is to target improving the health of those with excess weight through the beneficial eVects of physical activity rather than striving for unrealistic body habitus transformations by significant reductions in energy intake.11 Physical fitness, of which habitual physical activity is a major determinant, confers protection from cardiovascular and all cause mortality in the presence of overweight and obesity.12 Although the primary prevention and reversal of obesity is optimal, these goals may never be achieved in the industrialised world. A more realistic health promotion strategy is to encourage participation of the overweight and obese in lifestyle physical activity that is accumulated throughout the day to achieve healthier body weights.11 13 The purpose of this paper is to present evidence on the important role that lifestyle physical activity has in achieving and maintaining a healthier body weight through its favourable influence on the cardiometabolic risk factor profile in overweight and obese adults. Methods of systematic review Recently a plethora of literature has been published on the role of physical activity in the treatment of the overweight and obese. The extensive reference lists contained within these documents were scrutinised by the authors for relevant articles to include in this paper on the role of lifestyle physical activity in mediating a healthier body weight in the presence of overall adiposity. These reports included the National Institutes of Health Obesity Education Initiative (OEI),14 in which panel members con-
Lifestyle physical activity for weight loss in the obese
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Table 1 World Health Organisation classification scheme for overweight and obesity by the body mass index with associated disease risk3 Classification Underweight Normal Overweight Obesity Extreme obesity
Obesity class
Body mass index (kg/m2)
I II III
40
ducted a systematic Medline review from 1980 to 1997 on keywords relevant to the evidence based model for the treatment of overweight and obesity. Another key resource was the proceedings of the American College of Sports Medicine (ACSM) consensus conference,13 in which the authors expanded the scope of their reviews beyond the OEI in terms of years searched and appropriate keywords. Other reference lists consulted were the World Health Organisation,3 the American Medical Association,4 the Surgeon General Report,15 and the review by Dunn et al16 on the role of lifestyle physical activity in the treatment of obesity. In addition, a Medline search was conducted by the authors from 1997 to the present using various combinations of the major exposure measures discussed within this review. We found the literature on lifestyle physical activity and cardiometabolic health outcomes among overweight and obese adults to be promising but very limited, which is in agreement with others.13 16 Over the course of the year preceding the writing of this review, the authors subscribed to receipt of the current table of contents of scientific journals relevant to this topic. Finally, the authors’ personal files accumulated from their pertinent publications were examined,17–19 and experts were consulted for suggestions and recommendations about possible manuscript content. Definitions and basic tenets WHAT IS A HEALTHY BODY WEIGHT?
Accumulating scientific evidence indicates that the risk of death from cardiovascular disease and all causes increases throughout the range of overweight (BMI >25 kg/m2) and obesity (BMI >30 kg/m2) across the adult lifespan.20 21 Calle and coworkers21 reported the BMI range associated with the lowest mortality to be between 22.0 and 23.4 kg/m2 for women and 23.5 and 24.9 kg/m2 for men, whereas Stevens et al20 found the range to be between 19.0 and 21.9 kg/m2 for both genders. It is notable that the incidence of cardiometabolic disease begins to increase at a BMI well below 25 kg/m2.9 10 For these reasons, adults of all ages are recommended to strive for a healthy normal weight consistent with a BMI between 18.5 and 24.9 kg/m2.3 Table 1 shows the World Health Organisation classification scheme for overweight and obesity by BMI with associated disease risk. Given the alarming trend data provided in the introduction, most adults in the United States and other industrialised countries fall
outside the desirable BMI range associated with a normal weight. Many obesity related health conditions are ameliorated with relatively small changes in body weight.9–11 As indicated, physical fitness exerts a protective eVect even when excess adiposity is present.12 A realistic health promotion treatment strategy for the millions of overweight and obese persons is to strive for a healthier body weight within the confines of an otherwise insidious disease process. An ideal approach to achieve this goal is to increase overall energy expenditure through lifestyle physical activity. WHY LIFESTYLE PHYSICAL ACTIVITY? The traditional structured exercise prescription for becoming physically fit has failed dismally in motivating most adults to become habitually physically active.15 The fitness oriented exercise prescription advocated participation in 20–60 minutes of continuous aerobic exercise for three to five days a week performed at 60–85% maximal oxygen consumption (V ~ O2MAX), which is equivalent to 70–90% of the maximum age predicted heart rate or 7–10 metabolic energy equivalents (METs).22 Most Americans do not ordinarily exert themselves beyond 30–35% of the V ~ O2MAX!23 In recent years, it has become evident that the quantity of exercise needed for health benefit is considerably less than that needed to achieve physical fitness.15 22 In addition, participation in vigorous activity (>60% V ~ O2MAX) is associated with increased risk of injury and death for irregular exercisers and those with disease,24 25 which are common features of overweight and obese persons. These disclosures have led exercise and behavioural scientists to investigate innovative ways to encourage our predominantly physically inactive society to become less sedentary and more physically active. One encouraging approach in this regard has been the emergence of lifestyle physical activity. Dunn and coauthors16 have defined lifestyle physical activity as the daily accumulation of at least 30 minutes of self selected activities including leisure, occupational, and household activities that are at least moderate in their intensity. These activities may be planned or unplanned, structured or unstructured, and are part of routine tasks of everyday life. For the purposes of this paper, our focus will be on lifestyle physical activities that are of low to moderate intensity, defined as
